Drug Allergies - Exams and Tests

Exams and Tests

Your doctor will diagnose a drug allergy by asking you questions about the medicines you are or have recently been taking, your past health, and your symptoms (medical history) and by doing a physical exam. To find out which medicine is causing your allergic reaction, your doctor will consider:

• Your medicine. Some medicines are more likely to cause an allergic reaction than others.
• Whether you have a drug allergy or another adverse reaction to medication. You have more treatment options if you have an adverse reaction that does not involve the immune system.
• How many medicines you are taking. If you take several medicines, the medicine you began taking most recently is often the cause.

Your doctor probably will ask you to stop taking the medicine that is most likely to be causing the reaction. If this does not help, your doctor may ask you to stop taking other medicines, until you can find which medicine is causing the allergic reaction.

If your doctor cannot find out which medicine is causing the reaction, he or she may suggest a skin test. In a skin test, your doctor will place a small amount of medicine on or under your skin to see if your body reacts to it. However, a skin test does not work for all medicines, and you risk having a severe reaction.

Skin tests can diagnose allergies to:

• Penicillin, which is the most common cause of drug allergies.
• Insulin.
• Heterologous serum (used in the prevention or treatment of botulism, diphtheria, severe gangrene, organ transplant rejection, and snake and spider bites).
• Streptokinase (used to dissolve blood clots).
• Chymopapain (used for herniated discs).

Another way to find the cause of your allergic reaction is a medicine challenge. In a medicine challenge, you start by taking small doses of a medicine and slowly increase how much you take to see whether you have an allergic reaction. This challenge is usually done where emergency medical help is available and under the supervision of a health professional.

If you have medicine fever, serum sickness, or other complications, you may need more tests. These tests include a chest X-ray and blood tests to see how well your liver and kidneys are working.